BitLocker and the battery NomNoms

August 31, 2009 6:55 PM

How much will BitLocker eat my battery?

I've been using BitLocker on my laptop since Vista came out and continue to use it with the Windows 7 RC. In my experience the drive performance with and without BitLocker is about the same. What I don't know is if power usage is the same. I've read everything I can find about BitLocker and anything related to resource usage talks about disk reads and writes and system speed impact and how little impact there is. I can guess that since there is encryption and decryption that my battery life between charges is shortened. What I'd like to know is by how much. Are there any hard numbers from Microsoft or is there any way for me to calculate the extra load and figure out power usage from that?

posted by @homer to computers & internet (3 comments total)

I've been using BitLocker extensively on very low-power laptops, and haven't noticed any difference at all, in either performance or battery life. I'm no PKI expert, but I suspect that there really isn't any additional work going on at runtime - it's all at bootup.
posted by me & my monkey at 8:58 PM on August 31

There is additional work going on at runtime, but it's proportional to the number of bytes read from and written to disk. So if you're using your laptop to edit Word documents, you'll see almost zero impact. If you're watching video files stored on the hard drive, then there will be some impact due to additional CPU load.

For the I/O-intensive applications, the impact on battery life would be difficult to estimate. It is likely to vary significantly depending on the I/O access pattern and the power management capabilities of your CPU. The fact that you're having difficulty finding hard numbers may be a reflection of the fact that most of those numbers are in fact "soft." You'd probably need to carry out your own tests if you wanted useful numbers.

If you want to demonstrate worst-case CPU overhead, open a dos box and run "copy C:\some_very_large_file NUL". Run the test on a file which is larger than the size of your RAM.
posted by Galvatron at 9:50 PM on August 31

It will use extra CPU, but probably not enough to matter. Encryption algorithms are chosen to be fast to implement on general-purpose hardware. I use full disk encryption on all my laptops, and the batteries last long enough.

I have read that you can see a noticeable difference in battery life between a black screen with a flashing cursor and a black screen with a non-flashing cursor, though, so I won't say the impact to battery life is zero. I am just saying that for something as important as securing your data in the event that you lose your laptop, the cost is worth it.
posted by jrockway at 1:48 AM on September 1